System and method for heating skin using light to provide tissue treatment

ABSTRACT

A system and method for using a light source to treat tissue with NIR light. The operation provides for generating higher temperatures in deeper layers of tissue relative to shallower layers of tissue. The increased temperature in dermal layers can operate to induce collagen shrinkage, or remodeling. One of the light sources for providing a broad spectrum of NIR light is a filament light. The light from the filament lamp can be selectively filtered, and after filtering this light is applied to the skin, where the selective filtering can enhance the ability to elevate the temperature of deeper layers of tissue, relative to layers of tissue which are closer to the surface of the skin.

RELATED APPLICATIONS

The present application is a continuation in part of and claims benefit from U.S. patent application Ser. No. 10/789,139, filed Feb. 27, 2004, entitled SYSTEM AND METHOD FOR HEATING SKIN USING LIGHT TO PROVIDE TISSUE TREATMENT, which is incorporated herein by reference, and the Ser. No. 10/789,139 application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/540,981, filed Jan. 30, 2004, entitled SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS UTILIZING MULTIPLE LIGHT SOURCES, AND FILAMENT LIGHT SOURCE TO BE USED IN COMBINATION WITH THE SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS, which is incorporated herein by reference, and benefit from U.S. Provisional Patent Application Ser. No. 60/497,745, filed Aug. 25, 2003, entitled OPTICAL DEVICE FOR HEATING SKIN USING NIR LIGHT TO PRODUCE TISSUE SHRINKAGE, which is incorporated herein by reference; and the present application also claims the benefit of U.S. Provisional Application Ser. No. 60/601,352, filed Aug. 13, 2004, entitled METHOD FOR TREATMENT OF POST-PARTUM ABDOMINAL SKIN REDUNDANCY OR LAXITY, and is incorporated herein by reference; and the present application also claims the benefit of U.S. Provisional Patent Application Ser. No. 60/540,981, filed Jan. 30, 2004, entitled SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS UTILIZING MULTIPLE LIGHT SOURCES, AND FILAMENT LIGHT SOURCE TO BE USED IN COMBINATION WITH THE SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Devices using radio frequencies have been reported to be useful in heating skin at depths of a few to many millimeters. Such treatments may produce tissue remodeling or shrinkage, resulting in clinically useful changes in the morphology or appearance of the skin. The RF power can be problematic to apply to skin in that the contact electrode geometries and superficial hydration of the skin can greatly affect the coupling of power into the skin. Attendant complications include superficial burns, uneven application of energy. One reference which discusses the uses of a device for applying radio frequency to the skin is U.S. Pat. No. 6,453,202, entitled Method and apparatus for controlled contraction of collagen tissue

Some prior systems have provided for a combination of a light source in combination with use of RF electrodes to obtain relatively deep heating of dermatological issue. Additionally, some efforts have been directed toward developing systems utilizing a filament light source to apply light energy to the skin to achieve collagen shrinkage. However, prior systems have exhibited different significant limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view of dermatological tissue.

FIGS. 2 a-2 b show views of an embodiment of a system herein.

FIGS. 3 a-3 b show views of an embodiment of handpiece of a system herein.

FIG. 4 shows a cutaway view of an embodiment of a system herein.

FIG. 5 shows a graph illustrating filtering of a broadband spectrum, according to an embodiment herein.

FIG. 6 is a graph illustrating the absorption coefficient of water.

FIG. 7 shows a graph illustrating the penetration of different wavelengths of light in water.

FIG. 8 illustrates an example of a thermal profile in tissue being treated.

FIG. 9 illustrates the driving of a filament light according to an embodiment herein.

FIG. 10 illustrates an embodiment of a system herein.

FIG. 11 shows a embodiment of a system herein.

FIG. 12 shows an embodiment of a filament lamp of the present system.

FIG. 13A-D illustrate an embodiment with tailoring of thermal exposures through peak optical power control in one embodiment herein.

FIG. 14 shows an embodiment of a system herein with an anti-condensation plate bonded to the sapphire input surface, where the sapphire block transmits radiation to a treatment area.

FIG. 15 shows an embodiment of a system herein having the power supply mounted in the handpiece which applies the treatment radiation to the treatment area.

FIG. 16 shows an embodiment of a method herein for applying a therapeutic treatment.

FIG. 17A-C show an embodiment of a two tube cooling system herein.

DESCRIPTION OF THE INVENTION

One embodiment herein provides a number of advantages over some prior systems, such as no electrical contact with patient and reduced sensitivity to surface hydration. Also using a relatively broadband light source allows for tailored spectral profiles by filtering. Further, an embodiment herein provides for a broadband spectrum light source, which can be driven to output a range of different treatment fluences, and allows for control of the skin temperature to reduce the risk of unwanted thermal injury.

One embodiment of a device herein can use an incandescent lamp with significant optical output in the near-infrared range (NIR) from around 750 nm to 3000 nm. The lamp can be a quartz-tungsten-halogen lamp (“QTH”), but other, longer wavelength lamps may be useful (e.g., ceramic or carbon elements). A housing serves to couple NIR light to skin. The lamp is driven with high current supply, and could potentially utilize a modified version of the high voltage power supply described in the pending patent application filed Jan. 27, 2003 DERMATOLOGICAL TREATMENT FLASHLAMP DEVICE AND METHOD, U.S. application Ser. No. 10/351,981, which is incorporated herein by reference.

The desired skin absorbance profile is largely determined by water-based absorption in the NIR range, because the dermal layers targeted are generally located 1 to several mm deep. FIG. 1 shows a cross sectional view of dermal tissue. Layer 102 corresponds to epidermal tissue which has a thickness of approximately 100 μm, and this thickness can vary from patient to patient, and depending on the area of skin being treated. Layer 104 corresponds to the dermal layer which can have a thickness in the range of 1-5 mm, and this thickness can also vary from patient to patient, and depending on the area being treated. One aspect of the treatment herein is to provide for the heating of water molecules in the dermatological tissue being treated. This heating of the water molecules, will in turn heat adjacent tissue and where the temperature of the tissue reaches approximately 50° C. or above, thermal damage to the tissue can be observed. One aspect of the operation of the system and method herein is to heat collagen, which is a protein that makes up much the dermatological tissue, to a temperature in excess of 50° C. One of the effects of sufficiently heating the collagen, is to cause the collagen to change its characteristics as a result of thermal damage. This changing of the collagen characteristics is sometimes referred to as a shrinkage of the collagen, or remodeling, and this shrinkage of the collagen, can result in the reduction of wrinkles, or what appears to be a general tightening of the skin, in the area where the collagen has been sufficiently heated.

In general, different effects due to collagen shrinkage can be achieved by controlling the temperature profile in tissue being treated. In some circumstances a treatment may target both relatively shallow skin tissue, including possibly tissue in the epidermal layer, and to also heat deeper tissue in the dermal layer. In some other circumstances the treatment can be targeted at heating the dermal layer in the range of 1-6 mm, while minimizing the heating the upper dermal layer and the epidermal layer. Regardless of the specific treatment, it is generally desired to provide for some relatively deep tissue heating in the dermal layer.

To produce deep tissue heating and potential remodeling, or collagen shrinkage, a relatively large volume of skin must be heated. Associated thermal relaxation times are measured in 100s to 1000s of milliseconds. Existing art using lamps to heat skin is largely limited to volumes relaxation times below 1000 ms. Thermal relaxation time for deep bulk skin heating will allow exposures >1 second, in general to deposit sufficient NIR energy. Thus, as recognized herein a device may then be turned on for as long as several seconds to produce the desired thermal profile, said profile is based on the knowledge that tissue held at temperatures above 50° C., and preferably above 60° C., for any significant length of time will experience thermal damage, and in the case of collagen this thermal damage can result in remodeling or shrinkage.

A simple calculation provides a rough illustration of the heating required to produce collagen-changing temperatures. For this calculation consider a cylindrical slug of water 3 mm thick and 6 mm diameter and having a thermal relaxation time of approximately 10 seconds. So, heating such a volume could happen more or less adiabatically in a second. If the goal is to pre-heat skin (water) by 20 C in this time, this volume of water (approximately 0.1 cm3) would require (20 C)(4J/C*cm3)(0.1 cm3)=approx. 8J. That is 8J/1 sec=8 watts Assume the electrical to delivered optical efficiency of the light source is 5%, then 160 watts of electrical power is required. To obtain this efficiency, the source can be smaller in its dimensions (e.g., width) than the treatment spot size (which is approximately 6 mm in diameter) so, if it is a filament, it would ideally have a minimum electrical rating of at least 200 watts and be only a few mm in size.

In one embodiment, a source delivering peak powers in the NIR between 10 and 100 W per cm² is therefore required. Many generally available 600-1000 W quartz-tungsten-halogen lamps operated at rated power are unlikely to be useful as direct sources, since typical power densities at the lamp envelope are on the order of ˜1000 W/20 cm^2=50 W/cm^2, with the power density or irradiance falling rapidly with distance. The NIR portion of this results in power-in-band densities at the envelope in the low 10's of W/cm^2. Getting higher power densities can be achieved through utilization of different possible techniques. One possibility is using a filament light source for a limited life of operation and overdriving the filament lamp. Another option, which could be used alone or in conjunction with overdriving the filament lamp is collecting the output light from the entire envelope filament lamp and directing it to skin by means a reflector. Another option which could be used in combination with the above options, or alone, is employing water cooling of the quartz envelope of the lamp to enable the use of smaller lamp envelops.

Light sources other than filament light sources could also be used, but one of the challenges is finding an economical light source that outputs light of spectrum which is useful for heating water, or more specifically for outputting light across desired parts of the NIR range. For example, it is known that Nd:YAG laser light penetrates too deeply to effectively heat water in skin at appropriate depths to perform skin remodeling. The effective penetration depth is a function of the reduced scattering coefficient and the absorption strength of (mainly) water in skin. It is desirable to use somewhat more shallow penetrating light by seeking a waveband in which absorption is somewhat stronger than 1064 nm in water and in which scattering is no greater than the 1064 nm wavelength in skin. Light falling between 950 and 1400 nm has an absorption depth in water that varies between 1 and 28 mm. Taking into account scattering in a simple model, the effective penetration of NIR light in skin in this wavelength range varies from approximately 0.3 to 2.0 mm. Filtering the NIR light produced by a filament lamp can result in an effective penetration depth (function of scattering length and absorption depth) that can be tailored to aid in creating a desired thermal depth profile in tissue being treated. However, no matter what the spectral shape may be, the light intensity in tissue, and the absorption and, temperature profiles can only have a shape that is a sum of decaying exponential curves, since the absorption characteristic of each wavelength in skin follows a Beer's Law like profile. The consequence is that the thermal profile has the same basic shape, and that the spectral profile can only alter the general depth and strength of a Beer's Law-like thermal profile.

Useful bands for providing thermal remodeling can include 1150-1400 nm, and perhaps. 1500-1850 nm, and in fact light up to 3000 nm range can be beneficial. In the former, scattering is somewhat reduced with respect to 1064 nm light in water, and the absorption depth in water is deep to moderate, ranging from 4-12 mm. Considering the optical penetration depth that applies in skin, including the effects of scattering, the actual depth of penetration is approximately 3 mm. In the latter, scattering is significantly reduced compared to 1064 nm in water, and the absorption depth is relatively shallow (1-2 mm). Light from 1350-1550 nm is strongly absorbed and will only contribute to relatively deep epidermal heating.

In one mode of treatment the desired result is to produce higher temperatures in deeper thermal layers relative to the temperature at the epidermis. Heat is primarily deposited in a Beer's Law type profile, which subsequently transfers heat to the bulk of the skin. Absent some cooling applied to the surface of the skin, the application of light energy would create a temperature generally be higher in the epidermis than in the dermis.

FIGS. 2 a-2 b and FIG. 4 illustrates aspects of a filament lamp system 400 of an embodiment herein which can be used to deliver NIR light to tissue to provide treatment exposures. FIG. 3 shows an ergonomic handpiece 300 in which the filament lamp system 400 is disposed. FIG. 2 a shows a view of the filament lamp system 400 with some of the elements removed so as to be able to view elements in the system 400. FIG. 2 b shows a view of an assembled filament lamp system which would be disposed in the handpiece 300. In reviewing the FIGS. 2-4. Common reference numbers have been used to identify elements, where the same element is shown in various views represented by the figures. FIG. 4 shows a simplified cutaway view of the filament lamp system corresponding to FIG. 2 a. The function of the filament lamp system is described in detail in connection with FIG. 4 below. However, a brief discussion of FIGS. 2 a-2 b, and FIGS. 3 a-3 b is provided initially to give an overview of the system.

FIG. 2 a shows the system 400 the system 400 includes a filament lamp 402, and surrounding the filament lamp is a flow tube 408. A housing is 412 is provided, and light from the filament light is transmitted through other optical components such as a filter 422 and a sapphire block 420. The sapphire block 420 is cooled using thermoelectric coolers 428. The system also includes an LED 434 to indicate when tissue is being treated. FIG. 2 b corresponds to FIG. 2 a, but shows additional copper cooling blocks 438 secured against the thermoelectric coolers 428. These cooling blocks 438 can be supplied with cooling fluid, which operates to dissipate heat generated on the outer walls of the thermoelectric coolers 428.

FIGS. 3 a-3 b illustrate an embodiment of an ergonomic handpiece 300 with the filament light system disposed therein. The handpiece can consist of molded plastic pieces, or other suitable material. As shown the handpiece 300 has two molded plastic pieces 304 and 306. A cavity is formed between the molded plastic pieces, and the filament lamp system 400 is disposed in this cavity. Two apertures are providing the handpiece. One aperture is covered with a lens 302 through with light from the LED 434 is transmitted. The second aperture allows the sapphire block 420 to protrude from the handpiece so that it can be pressed against the skin. Epoxy can be applied to the seam between molded plastic pieces and the sapphire block to improve the seal between the sapphire and the plastic.

FIG. 4 shows a simplified cut away view of the system. The system includes a filament lamp 402. This filament incandescent lamp is an incandescent light source, and includes a filament 404. The filament lamp includes a quartz tube 406 in which a gas is disposed. In one embodiment the quartz tube 406 has a diameter of 10 mm. The length of the filament itself is approximately 22 mm, while the overall length of the lamp is approximately 4 inches. In order to obtain the desired light output the filament can be of a diameter of approximately 0.75 mm, and formed in to a helical shape having approximately 7 turns. The quartz tube 406 of the filament lamp is disposed within a flow tube 408 which can be formed with a transparent material such as glass or Pyrex. A fluid such as water is disposed within the cooling annular region 409 between the flow tube 408 and the quartz tube 406. This water can pumped through the annular flow region 409 by a pump and cooling system. In one embodiment the diameter of the flow tube 408 is 11 mm. Thus, the annular flow region 409 provides a spacing of approximately 0.5 mm between the outer wall of the quartz tube 406 and the inner wall of the flow tube 408. The water disposed in the flow region 409 can serve two purposes. One purpose is to cool the filament lamp. Given the relatively high power of the lamp, in one embodiment the filament lamp has an electrical rating of 400 W, and the small diameter of the lamp, and the confined geometry of the handpiece, traditional air cooling of the filament lamp is not possible. A second function of the water is to filter out some of the wavelengths of light generated by the filament lamp (through absorption). The amount of light filtered can be varied by providing flow tubes 408 with different diameters. In one embodiment different interchangeable handpieces could be provided where the systems disposed in the handpieces provide different thickness for the water envelop in the annular flow region 409. As the thickness of the water, which forms an envelop around the lamp is increased, the light transmitted through water will be subject to more absorption in the water, and thus less of the light at wavelengths which are absorbed by water will be transmitted through the flow tube 409. An umbilical connector 410 will transmit electrical power and coolant fluid to the system 400.

The filament lamp and the flow tube are disposed in a housing 412. The housing can be formed of a metal such as aluminum. The inner wall of the of the housing can be coated with a highly reflective metal, or it could be highly polished aluminum. In one embodiment a highly reflective gold coating is provided, where gold is used because it is highly reflective for NIR light. The housing is provided with a small aperture 414 which allows for a photodetector 416 to be disposed such that it can sense the light output power transmitted by through the flow tube 408. Depending on the sensitivity of the photodetector, and the output power, the photodector can be provided with an attenuator 418. The reflective housing is coupled to a sapphire block 420. A filter 422 can be provided such that additional undesired light can be filtered out prior to transmitting light from the reflective housing 412 into the sapphire block 420. In one embodiment the filter 422 is a non absorbing NIR and IR transmitting wavelength filter. The interface between the filter 422 and the sapphire block 420 is provided with an antireflecting coating 424 on the surface of the sapphire block to minimize power loss which can occur as light is transmitted through the filter 422 into the sapphire block. The lateral sides of the sapphire block 420 can be coated with metal surfaces 426. These metal surfaces should be as reflective as possible to minimize losses as the light is transmitted through the sapphire block. It should be recognized that an embodiment of the system might be implemented without the metal coating on the sides, and the total internal reflection of the sapphire block could suffice, so long as other elements were not in direct contact with the sapphire block. In one embodiment the metal used is Aluminum, as this metal has reasonably good reflective properties and easily adheres to the surface of the sapphire block. A cooling system is provided to control the temperature of the sapphire block, and the system can use thermoelectric coolers disposed on the metal surfaces 426. These thermoelectric coolers 428 operate to control the temperature of the sapphire block 420. The operation of thermoelectric coolers, which is known in the art, is such that by application of the electrical current to the thermoelectric cooler, one side of the thermoelectric cooler can be made cooler, while the other side of the thermoelectric cooler becomes hotter forming an electrically driven heat pump. In the embodiment shown, the cool side of the thermoelectric cooler is adjacent to the sapphire block. Additionally, although not shown in FIG. 4, cooling fluid can be used to remove heat from the side of the cooler which is not adjacent to the sapphire block 420. The sapphire block could be replaced with a block of different material, which would form a lightwave guide. Sapphire is, however, a desirable material for the system as it is a good transmitter of light, and it is also a good conductor for heat. In operation the outer surface 430 of the sapphire block is pressed against the area of the patient's skin 432 which is to be treated. The light 436 from the filament lamp is then transmitted into the patient's skin.

As discussed above the umbilical cable connects to the lamp system to provide control signals, electrical power and cooling fluid to the system 400. FIG. 10 provides a view of an embodiment of a system 1000 herein. As shown the system 1000 includes a main console 1020. Although the main console is shown as a single unit, it could in fact be multiple components connected together. The main console includes a controller 1004 which controls the overall operation of the other components of the system 1000. A power cord 1018 is provided to receive AC power, a power supply which can include a high voltage power supply (HVPS) 1002 for driving the filament lamp, provides power to elements of the system 1000. The main console also includes a user interface. In one embodiment this user interface 1008 is a touch screen display, and the controller is operable to drive the user interface 1008 to display different screens where a user can input treatment parameters. A cooling system which controls the temperature and flow of fluids which are used to control the temperature of components in the hand piece 1014. The power for driving the flashlamp, control signals and cooling fluids are delivered to the hand piece via the umbilical cable 1012. The umbilical cable is connected to the main console via connector 1010. This connector can include multiple connectors to allow for multiple hand pieces to be connected to the main console at different times. The controller operates to recognize the handpiece which is selected by a user, and to provide appropriate user interfaces and controls the selected hand piece which is being used to apply a treatment. An activation switch 1016 such as a foot pedal is provided so that a user can initiate the driving of the light source by stepping on the foot pedal.

FIG. 5 illustrates aspects of the operation of the system 400. The trace 502 shows an approximation of optical spectral power which is generated by the filament lamp without any filtering. As is known a quartz-tungsten-halogen filament lamp outputs a broad light spectrum approximating a black body radiation. By using a relatively heavy gauge tungsten filament the amount of NIR light can be increased over thinner gauge filaments, for a fixed input power. This is because the temperature that the radiating filament operates at for the input power is lower for larger gauge wires, and as is known the radiation temperature determines in large part the spectral curve. In order to achieve deep dermal heating for example up to approximately 4-6 mm, without damaging or burning the more shallow epidermal layers of the skin it is advantageous to filter out wavelengths of the spectrum which could be absorbed by more shallow layers of skin. The filter 422 operates to filter out light in the spectrum below approximately 1050 nm. The trace 504 shows the effect of filter 422 on the light generated by the filament lamp. It should be noted that the rapid follow off of the power in trace 504 at approximately 1750 nm, is not in fact due to the filter 422, rather it is a limitation of the IR detector array used to measure the power output the filament lamp and in reality trace 504 would approximate the upper end of the trace 502. Trace 506 shows the irradiance of the light output where the filter 422 is filtering light below 1050 nm, and the water in flow tube is operating to filter out some of the light which is strongly absorbed by water. At approximately, 1450 nm, where water absorption coefficient of water is very strong, it can be observed that a large amount of the irradiance from the flash lamp is filtered out. It should be noted the shown rapid fall off of trace 506 at approximately 1750 nm is due in large part to the limitations detector used to measure the power, and in fact a more gradual decrease in the power would be present above 1750 nm. Depending on the desired treatment, systems providing for a thicker or narrower water envelop around the quartz tube of the filament lamp can be used. Where heating of shallower layers of the dermis, or possible parts of the epidermis is desired the thickness of the water envelop can be reduced by, for example, using a smaller diameter flow tube. This will result in less absorption, or filtration of light by the coolant water in the range of 1450 nm, and this light energy which is not filtered would then be absorbed in the shallower layers of the dermis and the epidermal layer. Where deeper heating is desired, then it can be beneficial to increase the absorption of the light in the range of 1450 nm to reduce the absorption of this energy in the shallower layers in the skin. This allows for ability to keep the more shallow layers of the skin relatively cool, in part by reducing the light energy which would be absorbed in the more shallow layers of tissue. This reduction of the light which would be absorbed in the more shallow layers, and the cooling of the sapphire window to dissipate heat in the shallow layers of the dermis and epidermis, while still providing light energy that will propagate to deeper layers of the dermis, enhances the desired result of heating the deeper layers of tissue relative to more shallow layers of tissue.

FIG. 6 shows a graph with a trace 602 showing the absorption coefficient of water. As would be expected based on the discussion of FIG. 5, water has as very strong absorption coefficient at approximately 1450 nm. FIG. 7 shows a trace 702 that corresponds to the depth of light penetration into water. This graph illustrates that by filtering out light in the range of 1450 nm and at wavelengths above 1850 nm much of the energy which would be absorbed by the water in the shallow layers of the dermis or epidermis is be removed.

FIG. 8 shows an idealized view of the temperature profile in dermatological tissue where an exposure treatment has been applied using a system and method herein. The goal of one treatment herein is to provide for heating in regions 802 and 804 to approximately 60° C. while regions 806 and 808 and 810 remain at much cooler temperatures due to the active cooling of the sapphire block and the filtering out of light which would be absorbed in the shallow layers of the dermis and epidermis. In one mode of treatment regions 802 and 804 would be in the depth range relative to the top surface of the tissue of approximately 1-4 mm.

To achieve the type of tissue heating described above consideration must be given to the temperature of the sapphire block and the driving of the filament lamp. When a user has activated the filament hand piece, by for example stepping on the activation switch 1016, the controller and power supply coupled to the filament lamp hand piece by the umbilical cable are activated to provide a treatment. In one embodiment the user will be able select an amount of fluence for a treatment exposure using the user interface 1008. Once the user has selected an amount of fluence, the controller will determine how long the filament light source will be activated to generate light to output the desired fluence. The system is designed to provide a fluence range of from 10 J/cm2 to 50 J/cm2 . Of course these amounts could be modified if desired. Once the user has selected the desired amount of fluence, the hand piece 1014 is positioned so that the sapphire window is against the area of skin to which the exposure is to be applied. The user can then step on an activation pedal which will cause the treatment to begin. Upon stepping on the activation pedal, an LED 434 will light to indicate that the treatment has begun and that the user should not remove, or move, the handpiece and sapphire window relative to the area of patient's skin being treated. Initially, the system will operate to apply electrical current to the thermoelectric coolers and the temperature of the sapphire block will be brought to a treatment temperature. In one embodiment the treatment temperature is 20° C., but this could be set to a different temperature. The cooled sapphire block will continue to be pressed against the patient's skin for the initial cooling period where the sapphire will operate to cool the surface of the patient's skin. In one embodiment this initial cooling period will last for period of approximately 1 second. After approximately 1 second the power supply will operate to provide electrical energy to the filament of the filament lamp for a period of time until the desired fluence as been delivered to the patient's tissue. Depending on the desired fluence light will be transmitted from the filament to the patient's skin for a period of time ranging from slightly more than 1 second, an appropriate minimum could be for example around 1.2 seconds, and an appropriate maximum could be around 5 seconds. As will be discussed in more detail below, the power supply will stop applying electrical current approximately 1 second prior to the end of the treatment exposure and the hot filament light will continue to emit light until it has cooled sufficiently. The amount of time for which the filament radiates after current application is stopped depends on the thermal mass of the filament and the operating filament temperature, and can range form 0.1 to 2 seconds. During the application of the light from the filament lamp, the cooling system including the thermoelectric coolers will continue to cool the sapphire block, ideally keeping the temperature at the initial treatment temperature. After the filament light has stopped outputting the treatment exposure, the cooling system will continue to cool the sapphire block for a post treatment exposure time period, and the sapphire block will operate to dissipate heat from the patient's skin. The LED 434 will remain lit through the initial cooling time, the time when the treatment exposure is being applied, and through the post cooling time period. By keeping the LED lit, the user will know not to remove the hand piece and the sapphire block until the treatment exposure has concluded, and the post cooling time period has ended. In addition to the LED turning off to signal the end of a treatment, an audible signal could be provide to indicate to user that a treatment has been completed.

FIG. 9 shows an example of the current and voltage used in driving the filament lamp. In driving the filament lamp, pulses of electrical current are used to drive the filament of the filament lamp. FIG. 9 shows the current output for driving a filament light source, and the corresponding power output 910 detected by the photodector which senses the power in the housing. In this example a filament light source would be driven with an initial pulse 908 of electrical current having duration of 100 ms, and a current amplitude of 50 A, and then subsequent pulses 902 and 904 of electrical current. Depending on the desired operation of the system pulse widths of a wide range of different widths could be used, and the frequency of the pulses could be increased or decreased. The long initial pulse 908 is used to initially heat the filament light source, and rather than using one relatively long pulse a series of shorter closely spaced pulses could be used. Pulses 902 show 0.5 ms pulses and 904 shows a 1 ms pulse, the duration between pulses can be varied based on a signal from a photodetector which senses the optical output power, and/or based on a voltage sensed across the lamp. In one embodiment for example the applied electrical pulse would be such the output of power from the filament light would be ±1.5% of 16 watts. Thus, when the photodector sensed the power output dropped to a threshold level a 0.5 ms pulse of 50 A would be applied to the filament light source. As shown in FIG. 9 each pulse of current would have result in a corresponding voltage applied to the filament light source. The system can operate such that toward the end of a 0.5 ms pulse, based on a sensed optical output power, or a sensed voltage across the lamp, a subsequent 0.5 ms pulse can be applied if the optical power or voltage has not reached some threshold value. Voltage pulse 914 and current pulse 904 illustrate a situation where two 0.5 ms pulses are applied to form a single 1.0 ms pulse. Of course a wide range of different approaches could be used to drive the filament lamp to output the desired power. The output power from the filament light source is shown in FIG. 9 as detected by a photodetector as curve 910. The area 912 is a break in the time line, during which additional pulses would continue to be applied to the filament light source. The operation of the filament light source is such that it will continue to output electromagnetic energy for so long as the filament remains sufficiently hot. Thus, the curve 910 shows that optical power continues to be output by the filament light source even after the pulses of electrical current are no longer being supplied to the filament light source. In the example, shown in FIG. 9 for example where the last electrical pulse is applied at 2.5 seconds, the filament light source would continue to output a significant amount of output power up to about 3.4 seconds.

The filament can also be driven continuously by a supply, it is not a requirement to pulse the filament current at intervals during the treatment. This was actually a method developed to obtain filament capability using the same power supply that drives flashlamps. Other variations and different methods could be utilized such as providing a higher current during the preheat phase of the pulse, in order to bring the lamp up to heat quickly. This could be combined into one long pulse with higher current in the beginning and lower current at the end. An alternate control method would be to control the voltage applied to the lamp. The voltage would ramp up at a controlled rate to limit the inrush current. Alternately the voltage control would be a step applied and the current limit of the supply would limit the current.

The above described operation of the power supply driving a filament light source, illustrates an aspect of an embodiment of the present system. Specifically, a filament light source is normally considered a relatively low current, low voltage device. However, the filament light source can be driven with the same power supply which is used to supply high current and high voltage that is required to drive a flashlamp. As describe above the ability to control the power supply to short pulses of relatively high current, allows for the controllable power supply to drive the filament light source in a manner for providing effective treatments.

In another embodiment of the system herein, the filament lamp could be driven with lower current power supply which would apply a more continuous, but lower amplitude current to drive the filament. As one of skill in the art will recognize a variety of different power supplies could be used to drive the filament lamp.

FIG. 11 shows a detailed view of an embodiment of system herein. Specifically, FIG. 11 shows a view of a high voltage power supply 1106 which could be used to drive the filament lamp 1104 in the handpiece 1102 in the manner described above in connection with FIG. 9. As shown in detail in the U.S. Provisional Application Ser. No. 60/540,981, filed Jan. 30, 2004, entitled SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS UTILIZING MULTIPLE LIGHT SOURCES, AND FILAMENT LIGHT SOURCE TO BE USED IN COMBINATION WITH THE SYSTEM AND METHOD FOR FLEXIBLE ARCHITECTURE FOR DERMATOLOGICAL TREATMENTS, which is incorporated herein by reference, the power supply is very controllable and can operate to switch between and drive different types of light sources. In one embodiment the power supply uses a controlled chopper circuit with an inductive filter element 1126, operating in a pulse width modulated controlled current mode (in which the current is controlled and the voltage is determined by the device impedance and the impedance of the filter). Power supply 1106 could be also operated in a pulse width modulated controlled voltage mode (in which the voltage is controlled and the current is not controlled) or in a controlled power mode (in which the voltage and/or current are controlled in a manner resulting in controlled power).

In an embodiment herein, the controller of the power supply 1112 receives signals originating from the user interface 1114 and possibly sensors in the hand piece management unit which can determine when the handpiece 1102 has been removed from a seated position, and based on these signals determines how to drive the filament lamp when the user activates the filament lamp, by stepping on a foot pedal switch for example.

The operation of the power supply will be described in the context of the situation where a user has removed the handpiece 1102 from a hand piece management unit, and initiated the activation of the filament lamp 1104 of the hand piece 1102. In this situation when the hand piece 1102 is removed from a resting or seated position and activated the filament lamp, the operation described above will be performed.

The energy storage capacitor 1122 is charged to by the main electrical supply 1134 to a level allowing the desired energy to be delivered without unacceptable lamp voltage droop, where driving the filament lamp, at the desired current. When switch 1124 is closed current ramps up current through the filament lamp 1104, inductor 1126, and switch 1124. When the appropriate output power or current is reached, the controller 1112 opens the switch 1124 and the current now diverts to the diode 1128. When the current flow or output power drops to an appropriate level the controller 1112 again turns on the switch 1124 and the cycle repeats until a pulse is complete.

This toggling of switch 1124 on and off during a treatment exposure results from the photodiode 1132, or use of a voltage sensing circuit, determining that the optical power has reached a maximum value, and in response the controller opens the switch, and when the optical power drops to a low target level the switch closes, which increase the current through the filament lamp. It should be noted that as discussed in connection with FIG. 9, one embodiment operates with a central target for optical power of around 16 W. However, the power supply operation could be adapted such that the power supply drove the filament to output both varying amounts of power and varying treatment exposures. Also the current sensor 1130 and photodiode 1132 can be used independently, or in concert to control the optical power delivered to skin.

FIG. 12 shows an embodiment of lamp herein 1200. Aspects of suitable QTH lamps are described above. As discussed above it is important to be able to obtain sufficient optical power from the lamp in order to obtain the desired heating. Many previously available filament lamps are of relatively large dimensions relative to a treatment exposure area, and it can be very difficult to utilize these previous designs to obtain the desired heating. To achieve higher power the dimensions of a filament lamp in an embodiment herein have been changed relative to previously available lamps. The elements of a lamp 1200 illustrated in FIG. 12 illustrate significant dimensions of the lamp. The lamp includes a tungsten filament 1202. A portion of the filament 1202 is disposed in a quartz tube 1204, and the area inside the tube is filled with a gas 1206 which can include halogen. The portions of the filament that are outside of the tube 1204 can be partially sealed in tabs of the quartz tube which are not shown, and these tabs could be used to physically and electrically coupling the lamp 1200 with the other elements of the system. In one embodiment the length of the tube 1204 is about 2.4 inches (60 mm). In one embodiment the diameter of the filament is 0.75 mm, but a range of different thicknesses could be used. A center portion 1208 of the filament 1202 is formed in to a helical coil shape. In one embodiment the helical coil shape has a diameter 1210 which is approximately 6 mm. In one embodiment the tube diameter 1212 is approximately 10 mm. The ratio of the diameter of the tube 1204 and the diameter of the helical coil 1208 is 10:6. This ratio is very different that previous filament lamps where a ration of greater than 10:1 is very common. Generally, filament lamps utilize air-cooling. Where air cooling is used it is important to maintain a sufficient area for cooling the lamp, and generally one way of ensuring sufficient area is to maintain relatively large tube diameter relative to the diameter of the coil. Generally as the ratio of the tube diameter to the helical diameter gets below about 5:1 it is believed that air cooling will no longer be sufficient to cool the lamp, when it is driven at currents which are necessary to output the optical power required for the thermal treatments described herein, and as the ratio becomes less (for example the 2:1) as is the case described in connection with the lamp 1200 shown in FIG. 12 the cooling issues must be addressed, and the required energy fluences are obtained.

Given the ratio of the diameter of the tube relative to the coil in the embodiment of the lamp discussed above, and the amount of current which is used to generate a treatment exposure, traditional air cooling would not be sufficient to keep the lamp cool enough so that it would not become damaged and fail. Thus, the flow tube and liquid cooling discussed above is utilized to cool the lamp.

It should be recognized that the filament light source discussed herein is advantageous over some other light sources in that it is relatively inexpensive, and outputs a broad spectrum of light in the NIR range. At present flashlamps do not appear to provide as good a source for producing a broad range of power in the NIR spectrum, but some flashlamps might be suitable to produce such a range of light, and could be considered for use in a system for providing deep thermal heating.

As discussed above, some embodiments herein provide a method which uses externally applied electromagnetic radiation to produce heating for a controlled amount of time in skin. The thermal profile created by an embodiment of a system herein is such that the epidermal temperature is lower than the dermal temperature (e.g., shallower layers of skin are cooler than portions of the deeper layers of skin). This thermal profile provides a thermal gradient with a continuous variation in temperature as a function of skin depth, in which the superficial layers of the epidermis and dermis are at lower temperatures than portions of the deeper dermis. The epidermal temperature is held to a safe level while the dermis is heated by the electromagnetic (EM) radiation. It should be noted that EM radiation includes a wide range of different wavelengths of energy which can range from very short wavelengths, such as optical energy, to much longer wavelengths in the RF range.

In one embodiment optimal heating is produced through control of the absorption depth profile associated with the penetration of the applied EM radiation to the skin. The temperature profile, and its duration, affect the lax skin in such a way as to reduce, or reduce the appearance of, or otherwise tighten the appearance of, the excess skin. Desired depth profiles produce significant temperature rises in the range of 1 and 5 millimeters.

In one embodiment peak dermal temperatures are at least 40 C, with practical ranges falling between 40 and 70 C, and duration of the EM exposure ranges from 1 to 20 seconds. The time and temperature history during the exposure determines the degree to which redundant skin is effected, and therefore the degree of reduction, or the appearance of reduction of the redundant skin.

The depth of dermal heating is determined by the penetration of the applied infrared radiation, and generally not by thermal diffusion, because the optical penetration depth significantly exceeds the thermal diffusion length; or put another way, the time of exposure to EM, while relatively long and measured in seconds, is still short compared to the thermal relaxation time. The depths of heating in the skin are measured in mm, while the lateral extent of the heating in the skin is largely determined by the footprint, or area, of the contact waveguide/light channel which is delivering the treatment energy to the skin.

Penetration of NIR optical radiation is determined in large part by the wavelength filtering. In one embodiment treatments can be performed with filtering that is bounded on the short wavelength side by a 1050 nm long wave pass filter, and by the cooling water annulus having optical thickness of approximately 0.5 mm, where the water annulus strongly attenuates NIR radiation between 1400 and 1550 nm, and beyond 1850 nm.

For example in one embodiment the treatment footprint, or output area of the sapphire block 420, measures 10×15 mm. With the filtering and this treatment spot size, maintaining the area of the sapphire block which is in contact with the treatment area at 20° C. provides adequate epidermal safety/protection for a wide range of treatment fluences.

In some embodiments treatments can be applied without pain management (without need for pain killers) and such treatments can be applied in a stamping mode, with the contact area of the sapphire block held in contact with skin through a single exposure cycle (pre-cool, exposure, optical “cool-down”, post-cool). Where in one embodiment the pre-cool would be achieved by placing the cooled sapphire window in contact with an upper surface of the tissue being treated; the exposure is achieved by driving a filament lamp with electrical current; the optical cool down occurs when the optical energy decreases as a result of stopping the electrical current being applied to the filament; and the post-cool down is achieved by keeping the cooled sapphire block in contact with the tissue.

Treatments can be performed on all flat, or low curvature, portions of the face (forehead, temples, cheeks, neck). Care should be taken on high curvature portions of the face (mandibular line, nose, ocular orbit) because where the contact surface is rigid contact cooling is harder to achieve when the targeted treatment area is curved and rigid. In such areas consideration should be given to avoiding treating such an area, or a contoured contact surface or other cooling means should be used to cool the skin.

Without pain management or medication, patients can be treated with fluences at or near 32 J/cm². Typically, such treatments consist of one complete “pass”, or at most two, where a pass consists of covering the entire area to be treated with single adjacent exposures. In one embodiment, mild pain management is utilized with sedatives, such as Vicodin or Valium, in combination with analgesic pain relievers (such as non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen) and more aggressive treatment parameters are used. In some cases alternative pain medicine may want to be considered for use in place of the NSAIDs, because for some treatments, the anti-inflammatory effect of the NSAIDs may undermine the treatment. In one embodiment as many as 4 four passes are used with each application of energy, or pass, providing in the range of 40-45 J/cm². It should also be noted that different fluences can be used for skin on different parts of the body. For example, skin on the forehead and temple areas, can be treated with less fluence than areas of skin on the neck.

Single exposure durations can range from 1 to 10 seconds. For the nominal delivered optical power of approximately 10 W/cm², exposures are typically between 3 and 5 seconds. Time constants associated with the volume treated in one exposure are many seconds. If adjacent areas are treated consecutively, thermal build-up may produce unintended high temperatures. It therefore may be desirable to treat an entire contiguous area by means of applying exposures to non-adjacent positions, returning to fill in untreated areas. Alternatively, separating adjacent exposures by lateral distances of a few millimeters will allow thermal zones to have minimal overlap and avoid over-temperature/over-exposure. More aggressive treatments may proceed by intentionally overlapping consecutive treatment sites in such a way as to build up subsurface temperatures. Thermal relaxation times of the treated tissue are in the range of 1 to many seconds, so that the interval between successively applied treatment sites is sufficiently short that the tissue temperature rise persists long enough that the temperature can be increased at depth by applying overlapping treatments.

Alternative treatments may use lower fluences and many exposures. Examples might include from 2-10 passes at a fluence tolerable without pain management; such a fluence could be at or below 32 J/cm².

Tailored Thermal Exposures and Thermal Injury

In one embodiment herein, an aspect of the treatment is to create thermal tissue damage or injury from the delivered infrared exposure. However, it can be advantageous to deliver the infrared exposure in a controlled manner. Thermal tissue damage is generally a function of the time-temperature history of the tissue.

In the theory of selective photothermolysis (SPT), the pulse duration of the applied radiation and the characteristic thermal relaxation of the target tissue determines the target tissue temperature-time history, and the associated thermal injury. For some treatment applications a general principle is that for effective tissue damage, without collateral damage to surrounding tissue, the pulse width of the applied radiation should be on the order of, or shorter than, the target absorbing structure's thermal relaxation time (defined as the characteristic time for the temperature difference between the structure or volume and its surroundings to decrease by a significant amount) where the pulse time is in this range it can then be used to estimate the temperature rise of the target tissue as an adiabatic temperature rise due to the heat generated by direct absorption of the applied radiation by the target.

An embodiment of the present invention utilizes an approach which is somewhat different than SPT, in that it delivers energy which results in general heating of volume of tissue, and is not particularly selective so as to provide for treating primarily a targeted structure in a volume or area of tissue. Where considering volume heating, tissue damage may be described as occurring through an arbitrary temperature-time history experienced by the particular volume of tissue. In one treatment of thermal tissue damage (See, e.g., Markolf H. Neimz, “Laser-Tissue Interactions, Fundamentals and Applications” pp78-80, Spreinger-Verlag Berlin Heideberg (1996) which is incorporated herein by reference) the degree of cell or tissue damage is represented by a normalized Arrhenius time-temperature integral that varies between 0 and 1: C _(damage) [t]=1−exp[A∫exp(−ΔE/RT)*dt]

The degree of thermal injury to tissue can be produced by any number of thermal histories, represented by a time dependent temperature function T=T(t). The temperature function T is in turn determined by the applied radiation intensity, the absorption characteristics of the target (and surrounding) tissue, and the thermal diffusion and transport character of the target and surrounding tissue.

U.S. Pat. No. 5,885,274, entitled Filament Lamp for Dermatological Treatment, describes using an energy source to produce a thermal injury in skin by employing transient temperature spikes (one or more) that are short compared to the thermal relaxation time. In U.S. Pat. No. 5,885,274, infrared light from a filament lamp is used to produce temperature spikes in skin that may be relatively short. In an embodiment of system, such short period pulses would also produce rapid dermal temperature spikes, followed by a relatively long interval during which the temperature slowly decreases. Since the Arrhenius integral is exponentially dependent upon temperature, it could be problematic to create a measured dose of thermal injury in this way, particularly since the size of the temperature spikes may vary or may not be easily measured.

In one embodiment herein when a target amount of thermal injury is desired in a large tissue volume, the system operates to produce a relatively small temperature rise for a relatively long period of time. In some applications an embodiment herein can operate to control the temperature in such a way as to produce a constant temperature over the exposure duration by varying the applied radiation power appropriately. In this way, a desired level of thermal injury can be produced using lower peak temperatures, and use of longer lower temperature pulses is generally more controllable than shorter, higher temperature exposures.

In general, it may be advantageous to control temporal changes in the applied radiation intensity on time scales shorter than, comparable to, and even longer than, the target tissue volume thermal relaxation time. Having arbitrary control over the applied radiation intensity as a function of time allows for control of the thermal injury. This may also be used advantageously for pain management.

Operation of an embodiment herein has shown that a fixed applied radiation power for a duration of time resulted in steadily rising temperatures throughout the treated volume, where the treatment volume corresponded to a relatively large volume of skin. This is because the thermal relaxation time of the target volume is large, on the order of 10 seconds, so that even many seconds of exposure results in a continuously increasing temperature profile 1302 over time in the tissue area being treated (see FIG. 13A). The result is that the thermal damage is increasing with time, potentially rapidly as the Arrhenius damage integral depends exponentially on temperature. Additionally, the level of pain increases sharply as the temperature crescendos at the end of the exposure.

In FIG. 13A applied EM power 1304, which could be EM power from a filament lamp, and the subsequent heating profile 1302 of a volume of tissue are shown. In this initial simple case, the applied EM power is fixed at a constant level of P₁ for an exposure time t_(e). The temperature of the tissue volume rises above a minimum therapeutic temperature T_(min) and past the ideal upper therapeutic limit of T_(max). The duration of time at which the tissue is exposed to temperatures above the minimum therapeutic temperature (T_(min)) is the treatment duration, designated as t_(t). The tissue is then exposed to undesirably high temperatures for some duration, said time designated as t_(over). Typical treatment parameters for skin tightening treatments in this mode are: T_(max)=65 C, T_(min)=55 C, t_(e)=3 sec, t_(t)=1.5 sec, t_(over)=0.5 sec, P1=25 W (17.7 W/cm².) Note that in the example considered herein the area of where EM energy is applied to the skin is 1.5 cm²; which results in a power density of 25 W/1.5 cm² which gives a power density of 17.7 W/cm².

In order to avoid overheating, the power applied P₂ 1307, as shown in FIG. 13B, is decreased to avoid a temperature rise past the desired maximum temperature T_(max) (see FIG. 13B), the result is a temperature profile 1306 which provides a potential under-treatment, with the time-temperature integral and tissue damage being smaller than desired.

Applying a constant lower optical power 1307 avoids exceeding desired temperature treatment, but limits the time-temperature integral by reducing the total time, t_(t), that the tissue is above the therapeutic threshold, T_(min). A typical example would use: T_(max)=65 C, T_(min)=55 C, t_(e)=4 sec, t_(t)=1 sec, t_(over)=0 sec, P2=16 W (10.7 W/cm².)

An embodiment herein provides for producing the desired thermal effects, but with less pain during treatments, by appropriate design of the applied radiation temporal profile. In order to achieve the desired thermal injury without excessively overshooting the targeted maximum temperatures, and thereby potentially exceeding acceptable pain thresholds, an embodiment herein provides for control over the applied radiation temporal profile.

In one embodiment of the present invention, the closed loop optical power control was used to provide a two level power exposure profile 1308 in FIG. 13C. The profile 1308 shows the power output from the energy source. The higher initial power of profile 1308 causes the temperature profile 1310 for the tissue being treated to reach the desired target temperature rapidly. Subsequently, the power in profile 1308 is decreased to a value sufficient to maintain the desired temperature in the temperature profile 1310 for a desired amount of time, where the desired treatment temperature is in a temperature range between T_(max) and T_(min) and the desired temperature range could in one embodiment be significantly narrower than T_(max) and T_(min).

FIG. 13C shows a 2-level optical power profile 1308 applied to produce a relatively uniform temperature 1310 in the target tissue volume. A first EM power of P3 is applied for an initial time t_(e1), followed by a reduced power of P4 applied for a time t_(e2) where t_(e2) can correspond to a temperature treatment maintenance time period. The initially larger P3 raises the tissue temperature to the desired treatment temperature in therapeutic band between T_(min) and T_(max). The subsequent lower P4 maintains the tissue temperature in the treatment temperature range in the therapeutic temperature band. Typical 2-level parameters can be in the range of approximately: t_(e1)=1 sec, P3=25 W (17.7 W/cm²), t_(e2)=2.5 sec, P4=12 W (8 W/cm²), t_(t)=3 sec. Given current lamp technology and general treatment parameters most time values for maintaining the treatment temperature in the volume of tissue being treated will be at least 1.2 seconds, and typically will be 2 seconds or more.

In one embodiment an ideal radiation temporal profile would have the applied power initially high, and then continuously and smoothly decrease the power toward a constant level that would maintain the tissue temperature at a fixed value, or a value in a therapeutic range between T_(min) and T_(max). FIG. 13D illustrates operation of an embodiment herein where the applied power pulse 1312 is continuously and smoothly modified to achieve a temperature profile in the targeted treatment tissue at a therapeutic level between T_(max) and T_(min). While the applied power 1312 is shown as being continuously and smoothly changing during the time t_(e), the same effect could be achieved where power of the power pulse is adjusted to apply a discrete, but relatively small changes in the applied power where the small changes in the applied power are implemented over relatively short time intervals so that the applied power will approximate a smooth and continuously changing power profile as shown in trace 1312.

FIG. 16 shows an embodiment of a method 1600 herein. Initially a user who is applying a treatment to a target area can select a treatment parameter, and this could include selection of multiple different parameters. For example, for a treatment area which has a large amount of relatively thick lax skin a user might select a relatively high treatment setting. The user could be presented with a menu via the user interface 1008 of FIG. 10 which allows a user to select a total amount of energy to be applied, or a target temperature, or a length of pulse etc. In one embodiment a user could be presented with an option of merely selecting a level of treatment, where a level of treatment might very from 1 to 10 with 10 being the highest energy level for a treatment. Based on a user selected treatment parameter, the controller could refer to a look up table, or other data form which provides for an electromagnetic output profile, such as shown in FIGS. 13A-13D. Based on the selected treatment parameter the controller determines an EM treatment profile 1604. The sapphire block can be used to apply cooling to the treatment area to establish an initial treatment condition 1606. In one embodiment the initial treatment condition could be for example using the sapphire block in contact with the treatment area to bring the surface area of the treatment area to approximately 20 C. Based on the determined EM treatment profile, the controller would then drive the EM source, for example the filament lamp, to output an initial portion of the EM treatment exposure. In one embodiment this initial portion of the EM treatment exposure would be a temperature target EM output which operates to bring the treatment area to a desired treatment temperature in the a range between T_(max) and T_(min). After generating the initial portion of the EM treatment exposure, the output of the EM source is reduced to generate 1608 a treatment temperature maintenance EM output, where, as described above, this is generally a reduced EM output relative to the initial portion of the EM treatment exposure. As described above, the level of the power of the EM exposure output could be changed smoothly and continuously, or it could be changed over different time levels to different specific power outputs. After conclusion of the EM treatment exposure the method could further include applying a post EM output temp control to the treatment area. For example, the sapphire block 420 of the system could be kept in contact with the treatment area to lower the temperature of the treatment area after the EM exposure.

It should be recognized that while the power levels discussed above in connection with FIGS. 13A-13D are in the 10s of watts/cm² and higher, lower power levels could also be used. It can be advantageous to use lower power levels where less highly trained users are operating the system. For example, powers of up to 6 W/cm² may be used with exposures much longer that 5 seconds without reaching unsafe epidermal or dermal temperatures. This means that a range of treatment powers exist at which the sapphire block could be held in contact with skin for a long period, measuring many seconds or even minutes, elevating the dermis to some constant, relatively mild temperature distribution.

Filament Power Control & Safety Features

As described in detail above one embodiment herein provides for a filament energy source, where electromagnetic energy is generated by driving a current through the filament. In many embodiments it can be desirable to be able to have some control over the operation of the filament lamp.

Resistance Control

It can be desirable to heat the filament quickly when performing a dermatology treatment with a filament lamp, because controlling the optical power output by the lamp requires the filament to be hot enough to emit significant radiant power. In order to quickly raise the temperature of the filament, it can initially be driven with an electrical current capable of destroying the filament should it be applied to the filament for long periods of time.

One method of preventing overheating and subsequent failure of filaments is to measure or derive the filament resistance, which is a function of the filament temperature, and to use this resistance value as one input to control the power source. The pulse width modulation operation of the filament lamp by the HVPS can then be “resistance regulated”. No photometric monitoring is required in this mode. If photometric regulation is employed, resistance regulation may serve as a redundant check on the filament to protect against filament failure. In one embodiment the system includes a filament lamp which is connected to a power source, and the power source is electronically controlled to drive the filament lamp to output electromagnetic energy. The system also includes a sensor which outputs a signal corresponding to the resistance of the filament. In one embodiment the resistance sensor would operate to measure an instantaneous current through the filament, and an instantaneous voltage drop across the filament, and the resistance is determined by the voltage divided by the current. Although not shown in FIG. 11, a resistance sensor could, in one embodiment, be included in a system such as that of FIG. 11, where the resistance sensor would be coupled to the filament of the filament lamp 1104, and the output from the resistance sensor would be transmitted to the controller 1112. In one embodiment the resistance sensor could be used in place of photodetection, and in another embodiment the resistance sensor could be used in addition to photodetection. The power supply is operable to reduce the electrical current in response to a signal indicating that the resistance of the filament is increased beyond some specified value.

Filament Failure

In one embodiment, the filament lamp is driven by a high voltage power supply as described above; such an HVPS could also be designed to drive xenon flashlamps and Xe flashlamp driven lasers. As a result of using such a versatile power supply, it is possible that the voltage operating range for the HVPS will be quite high. In the event of a filament failure, the Xe/halogen gas in the filament lamp may continue to support current flow by establishing an electrical arc inside the tube. Uncontrolled arcing inside the lamp represents a potentially system-damaging event, while intense short-wavelength radiation from the arc represents a potential exposure hazard for the patient. One safety aspect of the invention is to use electrical pulses, where the pulses are short enough relative to a time period between the pulses, so as to allow any initial arcing to extinguish after a single pulse. The energy then available in a subsequent pulse is then low enough to avoid any hazard in the event of filament failure.

In one embodiment, one aspect of a safety circuit is that it senses when the lamp voltage (or resistance) has risen out of acceptable limits while it is being driven by the HVPS. This is also an indication of an open or high resistance filament.

Another aspect of the safety circuitry provides for a ground fault detector to remove power from the lamp when a ground fault is detected.

Anti-condensation Plate

As discussed above, it is desirable to protect the epidermis during treatments by controlling the epidermal temperature. In one embodiment as discussed above, a sapphire window is provided and is placed in direct contact direct contact with the skin. Electromagnetic radiation is transmitted through the sapphire block and applied to the skin. The sapphire window is temperature controlled using cooling devices in contact in contact with the sides of the sapphire window, maintaining a safe epidermal temperature. In some versions, thermoelectric coolers may be used. In other versions chilled coolant may be used.

In one embodiment it is desirable to have the epidermal control temperature be relatively high so that the dermal heating by the infrared lamp does not have to overcome a low dermal temperature imposed by the cooling. In order to reduce, or avoid, bulk cooling, that would have to be overcome by the EM source, sets the low end of the cooling temperature range at approximately 15 C.

On the other hand, using an epidermal cooling temperature that is too high potentially places a restriction on the type of cooling mechanism used to cool the sapphire window. Specifically, if the control temperature is higher than room temperature, or higher than the temperature of the console heater exchanger, uni-directional cooling cannot be used. This simply means that cooling mechanisms that can cool, but not warm (i.e. chilled coolants, uni-directional TECs), cannot be used.

This conflict between these two requirements on epidermal control temperature can be resolved by employing cooling mechanisms that are bi-directional (both cooling and warming capable). Such a requirement increases the system complexity and cost.

An approach taken in another embodiment is to simply operate at a temperature between the two limits described above (e.g., not so cool so as to create bulk cooling which might be difficult to overcome, and not so warm as to be of higher temperature than some environment where treatment environment is actually cooler than room temperature). In one embodiment the two limits are set in a range of practical epidermal cooling temperatures between 15 and 25 C.

Unfortunately, water condensation on the sapphire window/block is a potential problem for this temperature range. Water condensation problems are exacerbated by the following factors: (1) treatments require relatively long exposure times and near continuous contact with aqueous gels, (2) sufficient hermetic sealing of a hand piece to alone prevent condensation is difficult to achieve, (3) any condensation appearing on the sapphire is potentially very problematic given that water is the chromophore used in the treatments, (4) the spectral output profile, partially produced by filtering with the thin, controlled layer of water coolant surrounding the infrared lamp, may be adversely affected by any condensation which could in effect add additional filtering.

Previous approaches to this problem include insulating the cooled window from water vapor with a second window or optic. Typically the space between the cooled window and the insulating window is a gas or vacuum. U.S. Pat. No. 6,770,069, entitled Laser Applicator, by Hobart and Negus, describes a number of such approaches, and is incorporated herein by reference.

In order to reduce or prevent condensation an embodiment of the present invention employs a poor thermally conducting secondary window to support a thermal gradient at the input of the cooled window. The formation of condensation on the input surface of the sapphire window is thus prevented by holding this surface above the dew, or condensation, point. Typically, this requirement means at least a 25 C temperature is maintained at this surface.

An embodiment of a portion of a system herein is shown in FIG. 14. FIG. 14 shows a sapphire block 420 as described above, with an insulating layer 1402 coupled to the sapphire input surface 1404. The insulating layer 1402 can be an optically transparent glass window optically bonded to the sapphire input surface 1404 (where electromagnetic energy from the energy source is input to the sapphire block 420). The glass window operates as an anti-condensation plate, and supports a moderately strong thermal gradient across the material of the glass window 1402. The material insulating layer should have a low enough thermal conductivity such that even for a relatively low thermal loading on an input side of insulating layer a relatively large thermal gradient (ΔT) is maintained across the thickness of the insulating layer 1402. The glass window 1402 has a sufficiently poor thermal conductivity and thickness combination to allow for at least a 5 C temperature difference between the front (where the energy is input) and back (which is bonded to the sapphire block 420) surfaces of the glass window when thermal loads of at least 1 Watt are applied to the glass window (1 Watt represents a minimum in the thermal load that the lamp reflector air space presents to the input surface of the sapphire simply due to the warm air in the vicinity of the lamp.)

The glass chosen should have a poor thermal conductivity, and should also be thin enough to avoid making the optical assembly overly large or thick. Borosilicate glasses, such as Pyrex, is a good choice, while relatively conductive glasses, such as fused silica, are poor choices. Borosilicate glass from 1 mm microscope slide glass allows for at least an 8 C temperature difference (ΔT) at the input surface of the optical assembly, assuming at least a 1 Watt/cm² thermal load at the assembly input surface.

Thus, for an embodiment as shown in FIG. 14 where anti-condensation plate 1402 is optically bonded, such as by using an optically transparent adhesive, to the sapphire window 420, and the delta T of the glass (front-to-back) under a typical heat load is 8 C. A 20 C sapphire block then results in the glass window input face being held at about 28 C, which is safely above the dew point for almost any operating conditions.

A simple estimate of the temperature delta across piece of 1 mm borosilicate glass optically cemented to the sapphire window:

thermal conductivity (k): 0.8 W/m*degC. glass dimensions: 1.5 cm♯ ♭2 × 1 mm thick heat load to glass input surface (Q/Area):   1 W/cm♯ ♭2 Q/A = k ΔT/Δx ->> ΔT_(glass)~8C.

This same heat load produces only a 0.25 C temperature rise front-to-back across the thickness of the sapphire window (ΔT_(sapphire).)

An advantage of this using the insulating layer 1402 is that condensation is prevented while avoiding additional thermal load on the sapphire/cooling mechanism that other approaches might generate (such as, heating the input end of the sapphire.)

Cooling of Lamp Quartz Envelope

Some embodiments of the invention employ quartz tungsten halogen (QTH) lamps as the infrared light source. QTH lamps require a “halogen cycle” to prevent deposition of evaporated tungsten particles from adhering to the lamp interior wall. Aspects of this operation are discussed in “Illumination Engineering—From Edison's Lamp to the Laser” at pp. 208-211, by Joseph B. Murdoch, Macmillan Publishing Company (1985), which is incorporated herein by reference.

As discussed above an embodiment herein uses a liquid coolant element in contact with a QTH lamp envelope. The reasons for this type of cooling are: (1) the need to remove the bulk of the heat load dissipated in the hand piece itself, since most of the light/heat generated by the QTH lamp is not useful and desirably removed, and (2) use of a controlled thickness water annulus to perform part of the wavelength filtering function. The latter allows for strong water absorbing wavelengths emitted from the lamp to be removed. These strongly absorbing wavelengths if left unfiltered could largely result in undesirable epidermal heating.

A consequence of lamp cooling performed with water flowing across the lamp in an annulus is that the lamp exterior wall temperature is reduced because of the temperature of liquid water. Unfortunately, the halogen cycle does not work well for interior quartz wall temperatures below 500 K. Generally the halogen cycle begins area at around 250° C. and can range up to about 800° C. It has been found that lamps will degrade quickly at temperatures where the interior quartz wall is below about 500° K, under such conditions, darkening (due to tungsten deposits) the envelope wall and decreasing the optical output.

One solution is to decrease the lamp coolant flow to a point at which the cooling and wavelength filtering is adequately performed, but the lamp wall temperature is allowed to rise, while remaining comfortably below the boiling point of the coolant. This higher temperature improves the lamp degradation to a point at which operating the lamp becomes practical for medical applications (>10,000 exposures.) An embodiment herein provides for balancing multiple factors to determine the rate of coolant flow; these factors include: (1) the proper thickness for water wavelength filtering (between 0.25 and 1 mm, preferentially in the range of 0.5 mm), (2) heat removal from the lamp (removing a heat load of 50 W<heat removed<400 W), and (3), slow enough water flow to allow the temperature of the lamp wall to approach 100 C, the boiling point of the cooling.

An alternative embodiment could use a mixture of water and ethylene glycol or alcohol to allow the coolant temperature to rise even further, since water-admixture boiling points are higher than pure water. Another potential advantage arises from the use of water-admixture, instead of pure water. This advantage arises from the fact that for one embodiment using pure water provides that, for a desired amount of filtering, a thickness of water should be about 0.5 mm. In application it can be difficult to maintain manufacturing process to achieve a 0.5 mm thickness for the region where the water is disposed. Where water add mixture is used a the amount of filtering achieved per thickness of liquid is reduced, so the thickness of the liquid region can be increased to about 2.0 mm to achieve the desired amount of filtering, and with this increase in spacing it can be easier to maintain consistency in the manufacturing process, as tolerances for the thickness of the liquid region can be loosened.

One challenge with the above approaches is that to some extent they may limit the ability to cool the hand piece to a desired temperature. An embodiment is shown in FIG. 17A-B which provides for another way of providing for cooling and still allowing the quartz envelope to reach a sufficient temperature for the halogen cycle. Specifically FIG. 17A shows an isometric cutaway view of the filament lamp, which includes the filament 1702 and the quartz envelope 1704. An annular sleeve 1706 surrounds the quartz envelope. The annular sleeve, or tube, can be formed of different materials such as quartz, sapphire, or glass. The diameter of the annular sleeve 1706 is greater than the diameter of the quartz envelope 1704, such that a gap 1705 is created between the quartz envelope 1704 and the annular sleeve 1706. A second annular member 1708 is then disposed around the annular sleeve 1706. The diameter of the second annular member 1708 is of a greater diameter than the annular sleeve 1706. A cooling liquid, such as a flow of water 1709 can then be disposed in the gap 1707 between the annular sleeve 1706 and the annular member 1708.

The two tube structure of FIG. 17A is further illustrated in the cross sectional view shown in FIG. 17B. As shown in FIG. 17B a filament 1702 is enclosed by a lamp envelope 1704. The annular sleeve 1706 then surrounds the lamp envelope which forms a gap 1705 between the lamp envelope 1704 and the annular sleeve 1706. The gap 1705 can be filled with a gas, air or liquid which could be circulated, but in some embodiments it would not be circulated. The gap region 1705 operates to allow the lamp envelope 1704 to reach a sufficient temperature for the halogen cycle. The gap 1707 between the annular sleeve 1706 and the annular member 1708 can contain a flowing coolant. The lamp heat is radiated or conducted across gap 1705 and through the sleeve 1706 into the gap 1707 which is cooled by the flowing liquid. This allows high temperatures for the lamp envelope 1704 while the cooling of the handpiece can be achieved using the cooling fluid which is removed a short distance from the surface of the lamp envelope.

FIG. 17C shows an alternative embodiment 1710, similar to the two tube structure in FIG. 17A. However, embodiment 1710 utilizes a double walled lamp envelope which operates to provide an insulating gas region adjacent to the portion of the lamp with the quartz envelope tungsten filament halogen region. The filament 1712 is disposed in a first quartz envelope 1714, and an electrical lead 1728 is provided to the filament 1712. The halogen gas of the lamp is disposed in region 1716 inside the first quartz envelope 1714. A second quartz envelope 1718 is then provided around the first quartz envelop, forming a closed insulating gas region 1720 which is electrically isolated from the halogen region 1716. An outer annular sleeve 1722 is then disposed around the second quartz envelope 1718, and in the region 1724 between the second quartz envelope and the outer annular sleeve, cooling fluid flow for cooling 1726 can be provided. This design can allow for sufficient heating of the first envelope 1714 while the second envelope 1718 provides for containment of the cooling and filtering fluid away from the first envelope.

Shutter Element

An alternate embodiment of the filament lamp treatment device would use a shutter device to control the flow of electromagnetic energy from the lamp to the skin. The shutter would be located in the optical path between the lamp and the treatment area. When the shutter is in the closed position, it would prevent the treatment energy coming from the lamp from reaching the treatment area. In the open position the shutter would allow the treatment beam to reach the patient. The shutter device can be electromechanically actuated, and the duration that the shutter is open or closed could be determined by a timing circuit.

One of the inputs controlling shutter position could be feedback from a photodetector that receives at least part of its light from the treatment lamp. Alternatively, or in addition another input controlling shutter position could be a temperature measurement of the window in contact with the patient.

One benefit of using a shutter to control the transmission of electromagnetic energy to the treatment area is that the shutter provides a relatively simple mechanical structure, that allows the system to easily regulate the amount of energy transmitted to the skin. As shown in FIGS. 9A-9C and as discussed above, a significant amount of EM can continued to be emitted from the filament lamp for a time period after electrical current has stopped being applied to the filament. This can be a significant amount of energy which is many treatments should be taken into account. An alternative embodiment using a shutter, could utilize a power supply which operates to continuously apply current or pulses of current to the filament. In such a system the shutter could simply be opened to allow for the transmission of EM to the area being treated, and then the shutter could be closed to stop the transmission of EM to the skin. In such a system the lamp could essentially remain on for an extended period of time and the shutter would be opened and closed and as the device is moved over areas of skin to be treated.

Acne Treatments

Moderate warming of the epidermis and dermis can have a beneficial effect on acne by producing injury to sebaceous gland(s) (See, e.g., Javier Ruiz-Esparza and Julio Barba Gomez, “Nonablative RF for Active Acne Vulgaris: The use of Deep Dermal Heat in the Treatment of Moderate to Severe Active Acne Vulgaris (Thermotherapy): A Report of 22 Patients,” American Society for Dermatologic Surgery, Inc. 29:4 April 2003, which is incorporated herein by reference). More superficial and stronger skin heating produced using lasers such as the 1450 nm laser diode has been used to treat acne. Photoselectivity of the sebaceous gland may not be a requirement for such treatments. Confining thermal damage or thermal injury to the depths at which glands are located has been suggested as a mechanism for treating acne (See e.g., D Y Paithankar, E V Ross, et alia, “Acne Treatment with a 1.450 nm wavelength Laser and Cryogen Spray Cooling,” Lasers in Surgery and Medicine, 31:106-114, 2002, which is incorporated herein reference). In much of the previous literature regarding use of lasers for treating acne the general operational approach has been to apply millisecond long pulses of energy to the area being treated, where the energy operates to provide for relatively high, in the range of 80° C. temperatures, at relatively shallow, upper 0.5 mm, of the skin. Arrhenius thermal damage (as described above) can be achieved at lower temperatures than the 80° C. range, if the exposure duration is sufficiently long. Exposures of many seconds duration in the 45-60° C. range can be used to produce the thermal damage equivalent to much shorter exposure durations of pulses <100 ms with temperatures in the 80° C. range. The advantage is that lower temperature exposures may be performed more safely.

Thus, an embodiment herein can be used to apply lower temperature (45-60° C. range) acne treatment to a treatment area, where the combination of the energy source, for example a filament lamp, and the cooling of the sapphire block, and possibly using filtering to remove strongly absorbed wavelengths, allows for controlling and maintaining a treatment temperature in tissue being treated in a range of between approximately 45-60° C., for significant period of time. Where the treatment time for an application of EM energy would be greater than 1 second, and preferentially in a range of 2-5 seconds or longer to sufficiently damage the sebaceous gland and thereby reduce acne.

Hand Held Embodiment Including Power Supply

FIG. 15 shows an alternative embodiment 1500 of a system herein. The system 1500 provides for a simplified and lower cost design, which provides for lower lamp power. The system 1500 provides for an ergonomically shaped housing 1502, which can be shaped as handpiece suitable for extended periods of being held while the treatments are being applied to the skin. The other elements of the-system can be secured in the housing. The system can be powered AC power supply 1504, which receives AC power via a power cord 1506, which can be plugged into a conventional 120 volt wall outlet. Alternatively, a battery driven power supply could also be utilized, where the batteries could for example, be removably secured in the housing 1502. Aspects of a suitable shape for hand held device which includes all of the elements of an electromagnetic skin treatment system are described in more detail in co-pending U.S. patent application Ser. No. 10/794,882, filed Mar. 5, 2004, entitled SYSTEM AND METHOD FOR LOW AVERAGE POWER DERMATOLOGIC LIGHT TREATMENT DEVICE, which is incorporated herein by reference in its entirety.

The embodiment of system 1500 is particularly suitable for lower power applications utilizing infrared and/or near infrared electromagnetic energy. One example of such an application is the treatment of acne. Aspects of the treatment of acne are discussed in co-pending application Ser. No. 10/782,534, filed Feb. 19, 2004, entitled METHODS AND DEVICES FOR NON-ABLATIVE LASER TREATMENT OF DERMATOLOGIC CONDITIONS, which is commonly assigned, and is incorporated herein by reference in its entirety.

The system 1500 drives the filament lamp 1508 with a lower amount of electrical energy than more high power systems, whereby the optical power delivered is in the range of 2-10 W/cm². At this level of optical power the system 1500 is suitable for use by novice or untrained users. Specifically at the power density of 5 W/cm², repeated exposure would not heat skin unsafely with cooling. Further, at lower power densities, in the range of 3 W/cm², treatment could safely be provided without the need for epidermal cooling to protect the epidermis from overheating.

The exposure switch 1510 controls each exposure. Repeated exposures would be timed to maintain accumulated thermal doses below safe limits. Specifically, in one embodiment the power supply is provided with a simple processor which sets a maximum of electrical current which will be provided to drive the flashlamp per a given amount of time.

Given the significantly lower power levels of the system 1500 as compared with the other embodiments described above, the issues related to the cooling of the system and the skin are considerably simplified. As described, some of the higher power embodiments utilize a water cooling loop, with water flowing in an annular channel around the filament lamp. The lower power system does not require a water cooling loop. However, a water filter can still be utilized in the lower power system 1500. Specifically, in one embodiment a filter assembly 1512 is disposed between the filament lamp 1508 and the area of skin 1514 to which the electromagnetic energy is applied. The filter assembly includes elements selected to filter out specific ranges of electromagnetic energy emitted by the filament lamp 1508. One of the elements of the filter assembly is a thin layer of NIR-absorbing water. In one embodiment the filter assembly uses a water “sandwich” to perform this part of the filtering. Coatings applied to the exterior surfaces of the filter assembly perform the balance of the filtering. The absorbing nature of the water NIR filter portion places a requirement of heat removal on the filter assembly 1512. Because the overall heat load is relatively low, the mass of water and filter that must dissipate the absorbed heat is small. Thus, heat sinks 1516 can be included in the filter assembly. In one embodiment the heat sinks are provided with channels through which air flows, and the air current is created by a fan 1518 which is disposed in the housing 1502. The housing 1502 is also provided with openings 1520 to allow for air flow 1522 through the system 1500. Further, the power supply 1504 can be coupled with a heat sink 1524 to provide for dissipation of heat generated by the power supply. A reflector 1509 which is perforated for air flow can also be provided.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. This is especially true in light of technology and terms within the relevant art(s) that may be later developed. Thus, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

1. A handpiece for applying energy to a volume of tissue, the system comprising: an electromagnetic energy source energizable to output electromagnetic energy to be directed to the volume of tissue, the electromagnetic energy source disposed in a housing having an opening; a transparent window disposed in the opening, wherein electromagnetic energy is transmitted through the transparent window to the volume of tissue, and wherein the transparent window has a first thermal conductivity; a cooling device coupled to the transparent window; the transparent window including an input surface positioned to receive electromagnetic energy from the electromagnetic energy source, and a contact surface which is placed in contact with a tissue surface above the volume of tissue, the window contact surface to apply cooling from the cooling device to the surface of tissue and to transmit electromagnetic energy from the electromagnetic energy source to the volume of tissue being treated, and a transparent plate having a front surface positioned to receive electromagnetic energy from the source and a back surface bonded across the input surface of the transparent window, wherein the transparent plate has a thermal conductivity less than the thermal conductivity of the transparent window and wherein the transparent plate has a thermal conductivity, an area, and a thickness that results in a temperature difference (ΔT) of at least 5 degrees C. between the front surface and the back surface of the transparent plate when a thermal load of 1 Watt/cm² is applied to the front surface of the transparent plate.
 2. The handpiece according to claim 1, wherein the transparent plate is formed of a borosilicate glass.
 3. The handpiece according to claim 1, wherein the thermal conductivity and the thickness of the transparent plate results in a temperature difference (ΔT) of at least 8 degrees C. between the front surface and the back surface of the transparent plate when a thermal load of 1 Watt/cm² is applied to front surface of the transparent plate.
 4. The handpiece according to claim 1, wherein the transparent plate has a thermal conductivity of no more than 0.8 W/m*deg C.
 5. The handpiece according to claim 1, wherein the transparent plate has a thickness of at least 1 mm. 